This invention relates generally to heat exchangers, and more specifically to aircraft heat exchangers.
In aircraft engine oil cooling systems, oil is commonly pumped through an air-oil heat exchanger to remove excess heat and cool the engine oil. Engine fan air is utilized and provided as a cooling medium that flows into and through the heat exchanger to absorb and remove heat from the oil. The size of the heat exchanger is typically influenced by, for example, (i) the temperature of the cooling air, (ii) the temperature of the oil when it enters the heat exchanger, and (iii) the desired temperature of the oil when it exits the heat exchanger. With size constraints based on the temperatures of the system and fluids, the effectiveness or efficiency of the heat exchanger is also impacted by, for example, (i) the convection and thermal transfer of heat from the oil to heat exchanger surfaces, (ii) the conduction and thermal transfer of the heat through the material of the heat exchanger surfaces, and (iii) the conduction and thermal transfer of heat into the air of the heat exchanger. In sum, the convection of thermal energy to the air side of the heat exchanger is typically most limited and hence establishes the thermal energy transfer from the oil to air, thus cooling the oil.
To achieve thermal transfer between a hot fluid, such as oil, and a cold fluid, such as air, layers of the two fluids are stacked within a heat exchanger. The two fluids are kept fluidly isolated, but maintain thermal communication to transfer heat between the two fluids. Accordingly, to maximize thermal transfer, the greatest surface area of contact is desired, and thus the layering of hot and cold fluids is alternated in the stack of layers.